1. Field of the Invention
The embodiments herein generally relate to numerical methods, and, more particularly, to numerical methods for forest meteorology and acoustic computations and applications.
2. Description of the Related Art
Acoustic sensors are emerging as a key technology for providing battlefield situational awareness necessary to protect ground combat troops. Advantages of acoustic sensors include low cost, compactness, passive operation, low power consumption, and non-line-of-sight capability. Many new systems use acoustical arrays to detect, classify, estimate bearing, and cue narrow field-of-view (FOV) optics. Some new systems use multiple, networked arrays to track targets by bearing estimation and triangulation. At the same time, acoustic sensor performance is strongly affected by the atmospheric environment. It is anticipated therefore, that improved physics-based theory and computer models for meteorology coupled to acoustics (in and around forests) will contribute important information on the performance of advanced combat sensors, systems, and communications as well as the effectiveness of battlefield computer aids to increase situational awareness.
Some of the conventional techniques related to numerical models for forest meteorology include exponential or extinction profile models, which are formulated to predict one-dimensional (1D) wind speeds primarily in the mid-to-upper portion of the forest canopy. Unfortunately, these exponential or extinction profile models tend to be difficult to combine to observed or estimated wind speeds above the treetops or below the layer of leaves and branches. In addition, extinction profile models are typically not formulated to predict temperatures within and above forests, which are needed to compute sound speed.
Prior art related to the development of numerical model codes for forest meteorology were generally formulated to predict one-dimensional wind speeds and turbulence within and above uniform forest canopies. In these models, radiation and energy budget algorithms were not included to predict the heat source (temperatures and sound speed). In contrast, the three-dimensional Large Eddy Simulation (LES) model described by Albertson et al., “Relative Importance of Local and Regional Controls on Coupled Water,” (2001), did consider energy budget effects, however, this as well as other LES models are quite computationally intensive and are not within a computational framework that is most efficient for a rapid and reliable prediction of acoustic propagation in forest environments. In one further case, the prior art, as described by Meyers and Paw U, “Modeling the Plant Canopy Micrometeorology with Higher Order Closure Principles,” Agric. For. Meteorol., Agric. For Meteorol., 41, 143-63 (1987) and Pyles et al., “The UCD Advanced Canopy-Atmosphere-soil Algorithm:                Comparisons with Observations from Different Climate and Vegetation Regimes,” Q. J. Roy. Met. Soc. 126 2951-2980 (2000), are also quite computationally intensive. In general, their models offer much more information related to soil and plant physics than is necessary for the rapid and reliable prediction of sound speed in forests. These models, however, have been applied for the study of carbon dioxide and other trace gas emissions, which have a significant impact on large scale climate.        
Prior art related to ray path model codes for acoustic propagation and transmission loss generally assume homogeneous sound and wind speed fields (e.g., Moler CB and Solomon LP, “Use of splines and numerical integration in geometrical acoustics.” J Acoust Soc Am 48: 739-744, 1970; Hallberg B, Larsson C and Israelsson S “Numerical ray tracing in the atmospheric surface layer” J Acoust Soc Am 83: 2059-2068, 1988; Huisman W H T “Sound propagation over vegetation-covered ground,” Dissertation, Univ. Nijmegen, The Netherlands, 176 pp., ISBN 90-9003624-5 (1990), Huisman W H T and Attenborough K “Reverberation and attenuation in a pine forest,” J Acoust Soc Am 90: 2664-2677 (1991), and Salomons E M “Computational atmospheric acoustics,” Kluwer Academic Publishers, Dordrecht, 335 pp 2001). The advantage of the invention described herein is that the acoustic models are based on the principles and theory for geometrical acoustics for an inhomogeneous moving medium. Ray paths are thus computed as a function of range dependent wind and sound speed fields. These data are provided independently from 1D and 2D, physics-based, meteorological model for forests (Tunick A (2003a) “Calculating the micrometeorological influences on the speed of sound through the atmosphere in forests,” J Acoust Soc Am 114: 1796-1806, Tunick, A. (2003b) A two-dimensional meteorological computer model for the forest canopy. ARL-MR-569, US Army Research Laboratory, 2800 Powder Mill Rd, Adelphi, Md. 20783-1197, (2003), Tunick, A. (2004a): Toward improving the efficiency and realism of coupled meteorological-acoustic computer models for the forest canopy. ARL-MR-586, April, U.S. Army Research Laboratory, 2004). In addition, acoustic intensity due to geometrical divergence (i.e., energy loss due to spherical spreading) is computed as an inverse function of range and the height difference between two adjacent rays. At the same time, acoustic intensity gain (or loss) due to frequency-dependent ground effects are included in the model calculation. Note that while the acoustic numerical models embedded in this invention are much simpler than parabolic equation or fast field acoustic programs (West et al., 1991, 1992; Noble J M (2003) User's manual for the Microsoft window edition of the scanning fast-field program (SCAFFIP) version 3.0. ARL-TR-2696, US Army Research Laboratory, 2800 Powder Mill Rd, Adelphi, Md. 20783-1197. [Available from the DTIC at http://stinet.dtic.mil/str/]), ray path models have nevertheless been shown to be a practical and useful tool for analyzing and interpreting refraction effects on sound waves.
Other conventional models include first-order closure, physics-based models, which are formulated to predict two-dimensional (2D) wind speeds and turbulence within and above forest canopies. Here, radiation and energy budget methodologies are generally not included to predict the heat source (temperatures and sound speed). Additionally, second-order closure, physics-based models have been developed to predict one-dimensional (1D) wind speeds and turbulence within and above forest canopies. Again, radiation and energy budget methodologies are not included to predict the heat source (temperatures and sound speed). Furthermore, higher-order closure, physics-based models such as three-dimensional (3D) Large Eddy Simulation (LES) models have been formulated to predict 3D wind speeds, temperatures, humidity, and turbulence within and above forest canopies. Here, radiation and energy budget algorithms are sometimes incorporated to predict the heat and moisture sources. However, these models tend to be quite computationally intensive, especially with regard to turbulence and advection scheme methodologies. Also, they can offer much more information related to soil and plant physics than is necessary for the rapid and reliable prediction of sound speed in and around forest canopies.
Conventional techniques related to ray path model codes for acoustic propagation and transmission loss generally assume homogeneous sound and wind speed fields. However, forest stands are typically inhomogeneous, containing non-uniform distributions of canopy height and leaf area density. In addition, open fields, roadways, and buildings often border forests. Generally, the conventional techniques primarily show the development of forest canopy wind flow and turbulence models only. However, there remains a need for a forest meteorology and acoustic computation technique that takes into account horizontally non-uniform sound speed information.
Furthermore, an advantage of this invention over the prior art is that it combines the inventors' existing numerical models developed in accordance with the invention and those still in development into a comprehensive process, which includes input, memory and computing devices, numerical codes, and graphics display. The invention necessarily addresses both the thermodynamic and mechanical influences on sound speed within and above forest canopies. Numerical models are executed in a computationally efficient framework. Hence, the invention is a novel process to obtain rapid and reliable predictions of useful acoustic and meteorological information, which can be applied to the study of meteorological aspects of acoustic propagation within and above forests.